Switching circuit



Jan. 16, 1968 G. M. MEYERLE 3,363,615

SWITCHING CIRCUIT Filed Feb. 25, 1965 ATTORNEYS United States Patent 3,363,615 SWITCHING CIRCUIT George M. Meyerle, South Ozone Park, N.Y., assiguor to Network Research & Manufacturing Corp. Filed Feb. 25, 1965, Ser. No. 435,303 16 Claims. (Cl. 123148) ABSTRACT OF THE DISCLOSURE A switching circuit particularly useful for ignition systerns in which an inductive load such as the primary winding of an ignition coil is connected in series with a periodically and mechanically operated interrupter switch, and a normally open solid state bypass circuit is connected across the switch. The bypass circuit is adapted to close a predetermined time after opening of the switch to provide a shunt path around the switch and effect buildup of flux in the coil prior to subsequent closing of the switch.

This invention relates to solid state switching circuit systems and especially to internal combustion engine ignition systems and tachometers therefor.

In general, when using mechanical switches for periodic operation of circuits where the on time and off time are not necessarily equal, it is difficult to provide an extremely short off time without using a complicated and difiicult to track cam arrangement or using very close tolerances for the gap opening of the switch, such as the distributor points of an internal combustion engine.

In conventional internal combustion engine ignition systems, a high current passe through the breaker points or interrupter, the high voltage causing damage to the points and requiring frequent adjustment and replacement thereof. In prior transistor ignition systems or systems using solid state devices, the problem that has arisen is that the amount of sparking energy available at higher speeds is inadequate to provide the desired performance. Prior transistor ignition systems, in order to take advantage of low voltage devices heretofore available, have used a low inductance, high current arrangement. This has proved to be inadequate in cold-weather tarting when the battery voltage drops to as low as 7 or 8 volts. The amount of energy lost due to low voltage is considerably greater with a high current system than with prior ignition systems so that prior transistorized ignition systems would have considerably more trouble in starting the engine in cold weather. This is because the prior known transistor systems do not bypass the conventional limiting resistor in the battery lead.

Prior transistor ignition systems also have suffered because of use of reduced breaker point current in points designed for high current application. The reduced current caused deposit of non-conductive coatings on the points, resulting in non-uniform performance. As a result prior transistorized ignition systems have required the points to be changed due to the aforementioned non-conductive coatings. Points normally used in conventional ignition systems are designed for high current operation, e.g., in the range of 3 to 6 amperes. The voltage which is present in prior conventional ignition systems causes a high voltage to appear across the points, especially at low engine speeds. As the points open, the voltage rise time of the sparking voltage is very short. The points are almost closed fora very long period of time .at low engine speeds. This aforementioned high voltage appears across a very small gap, causing severe burning and loss of energy across this gap when needed for starting.

One of the objects of the invention is to provide a system wherein the energy supply of each cycle is initiated 3,363,615 Patented Jan. 16, 1968 mechanically and electronically rather than only mechanically.

Another of the objects of the invention is to provide an improved transistorized ignition system wherein optimum energy is available at all engine speeds.

Another of the objects of the invention is to provide a transistorized ignition system wherein improved breaker point life is obtained.

Still another of the objects of the invention is to provide a more stable operating tachometer using the output from the transistorized ignition system of the present invention.

In one aspect of the invention, the circuit having a periodically operated mechanical switch is used to control current or power to a load. A bypass circuit having a time delay means is provided around the switch so as to feed current to the load :a predetermined time after the switch opens. This time can be made quite short if desired. This bypass circuit has a transistor between the switch and load connected with a means to provide a forward bias to the transistor when the switch is closed.

In one form, the load comprises an ignition coil, and the switch is the breaker of the conventional ignition system. A reverse or back-biasing diode means or circuit is connected across the base and emitter of the transistor together with a reference between the base and ground, the reference being in the form of :a diode means or a resistor. When the breaker points are closed, the transistor is in a conducting state so that energy builds up in the ignition coil, there being a bias applied to the transistor so that it is conducting. Upon opening of the breaker points, the bias on the base-emitter junction is such as to interrupt flow through the collector-emitter junction. The transistor then is turned on before the breaker points c'lose again so as to provide a higher current level through the coil than would be the case if it did not turn on until the breaker points again close. The turn on or bypass of the mechanical switch is accomplished by a resistor-capacitor network of parameters to permit the spark to be completed and then to trigger a transistor circuit to bypass the mechanical switch. When the mechanical switch does close again, the bypass circuit is reset for the next operation.

In addition to the transistor ignition aspect, :a tachometer operating circuit can be connected to the transistor circuit. In one form, the tachometer circuit is arranged to produce a square wave which is differentiated and rectified to produce an R.M.S. voltage proportional to engine speed.

The above, other objects and novel features of the invention will become apparent from the following specification and accompanying drawings which are merely exemplary.

In the drawings:

FIG. 1 is a circuit diagram of one form of the invention.

FIG. 2 is a graph showing the relation of current to time in conventional systems and in the present invention.

FIG. 3 is an alternate form of tachometer circuit.

As an example of the invention, a source of DC (FIG. 1) is furnished to terminal 10 which feeds through resistor 30 and lead 11 to the induction coil 12 which may be the primary of ignition coil 13. It is to be understood that the ignition coil 13 may have a primary 12 and secondary 14 as shown, or may be of the autotransformer type (not shown).

Transistor 15 has a base 16, collector 17 and emitter 18. In the form illustrated, it is of the NPN type but a PNP type also could be used. In the latter instance, the position as indicated hereafter of the emitter and collector could be changed with the necessary reversal of the other portions of the circuit. For example, the connection at lead would be made negative, back or reverse bias diode 22 reversed and other points changed accordingly. Emitter 18 is connected by lead 19 through junction 23 to one side of a switch, interrupter or conventionalautomotive breaker point system 20. The other side of the breaker point system is grounded at 21. Reverse biasing diode 22 is connected between junction point 23 and junction point 24 for a purpose which will be described hereafter.

Reference diode means 25 may comprise three diodes connected in series, other combinations being possible. Base 16 of transistor is connected by lead 26 to junction point 27. Lead 28 connects the positive side of D.C. source 10 through resistor 28A to junction 27 and to junction point 24.

Describing the operation of this portion of the circuit, when interrupter 29 is closed, current will flow from source 11), through coil 12, through transistor 15, to junction 23, and through interrupter to ground 21, a forward bias being applied to base 16 through resistor 28Av The transistor 15 is in effect a closed circuit to the D.C. from source 10 to ground 21 because resistor 28A causes current to flow through :base 16 of transistor 15, resulting in current flow by transistor action between collector 17 and emitter 18 of transistor 15.

When interrupter or breaker 20 is opened, the voltage at junction 24 due to resistor 28A rises to approximately 2.5 volts or other predetermined reference voltage. The voltage at junction 23 due to current flowing from source 10 through resistor 29 and diode 22 will be approximately 3.2 volts, or a predetermined higher voltage than that at junction 24. This difference in voltage will place a reverse bias on the base-emitter junction of transistor 15, interrupting current flow through the transistor collectoremitter junction to open the DC path through coil 12.

The reference diode unit will insure that during the conduction period, the current required through resistor 28A will be employed solely to turn on or saturate transistor 15. There is no current during the on portion of the cycle through diode unit 25. The only time that current flows through reference diode unit 25 is from the time the breaker points open until conduction is established electrically as will be explained hereafter. In order to obtain approximately 2.5 volts to insure proper turnoff of the transistor, the diode unit 25 comprises three silicon diodes connected in series. It is to be understood that a resistor (not shown) could be substituted for unit 25, although such would not be as satisfactory because of dissipation of energy and heat.

It also has been found desirable to have sufiicient energy to provide a hot spark at all speeds in order to have optimum sparking conditions at all times. In a conventional ignition system, resistor 30 is connected in series with the ignition coil to limit current through the coil and to improve the current rise time characteristics at higher speeds. It can be shown that at high speeds the energy in the ignition coil will be reduced by a factor of as much as 80%. The current builds up slowly and the time that the points are closed at high engine speeds is very, very short.

Referring now to FIG. 2, the interrupter points close at time C and current will rise along the dotted line to level A where the breaker points open. In the presentinvention and as will be described later, the current is turned on electronically at time D and will rise along the solid line to level B which is above A. The time at which current is turned on after opening of the breaker can be made very small, for example, 100 microseconds. As is well known, current rise is dependent upon the time that the current flows through the coil. Thus, commencing flow of current through the coil in a much earlier time than hitherto possible will result in a higher current in the system at time of interruption.

The circuit for turning on the transistor electronically is shown generally in box 31. The purpose of circuit 31 is to increase the conduction time of transistor 15, the operation of the circuit 31 being as follows. Resistor 32 and capacitor 33 have a time constant which is just long enough for the time required for an adequate spark. Capacitor 33 has a charge built up thereon due to the voltage appearing at junction 23 through resistor 32 as the breaker points open. Transistor 34, which can be either a NPN or PNP device depending on source voltage and arrangement of 51 and 52, draws current through its base-emitter junction, It also would be possible to connect lead 42 to lead 37A so as to omit transistor 38. When using two transistors, an economy in parts results with the present state of the transistor art. The transistor 34 has base 35, emitter 36 and collector 37. Transistor action between the collector-emitter junction of transistor 34 will cause current to flow through transistor 38 having base 39, emitter 40 and collector 41. The current flowing through the base-emitter junction of transistor 38 causes transistor action to occur and current to flow between collector 41 and emitter 40 of transistor 38 which acts as a low resistance path between point 23 and ground 21. This takes place through lead 42, transistor 38, lead 43 to ground 44. Thus, at the completion of the time governed by the time constant of circuit 31, there will in effect he a closed path to ground in parallel with the open breaker points. Such will cause transistor 15 to conduct and store energy in the primary of ignition coil 12 for a period of time approximately longer than the time without use of circuit 31. Thus, the points 20 are bypassed electronically to ground to cause current flow through primary 12 of the coil even though interrupter 20 is open. When interrupter 20 now closes in a normal manner, such will discharge capacitor 33 through interrupter 20 and resistor 32 to reset the system so that it will be open for a very short period of time when the interrupter points break at the desired sparking time.

In addition to the transistor action in conjunction with the described ignition system, a tachometer or r.p.m. indicating arrangement can be operated, the preferred circuit being shown in box 45' (FIG. 1). The voltage waveform at junction 23 is one wherein the voltage is zero during the time the points are closed and with a voltage from 3 to 12 volts (depending upon the system). This in essence is a square wave function which when differentiated and rectified will produce an R.M.S. voltage proportional to the engine speed. Such is true of the present invention as well as prior transistorized systems. In the present invention, the transistor 50 of circuit 45 is used to amplify the peak value of the square wave voltage obtained, e.g., 3 volts, to 6 or 12 volts which is the battery potential commonly found in automobile batteryoperated ignition systems. This new square wave is differentiated by capacitor 53 and resistor 55. The differentiated wave is rectified by diode 54 and the rectified current connected to an R.M.S. meter 56 to provide an indication of r.p.m. Thus, circuit 45' will directly give the desired signal without use of multi-vibrators or the like. The system is not sensitive to breaker point bounce which gives erroneous readings at high speed.

FIG. 3 shows another tachometer arrangement in box 45 which could be substituted for the circuit in box 45. The circuit of FIG. 3 is connected to point 46 of FIG. 1 instead of point 23. In a normal ignition system, the voltage waveform at point 46 would be an exponential wave with zero points increasing to the off time of the system, and exponential rising characteristics approaching 6 volts during the on time of the system. At very high engine speeds with conventional ignition systems, the peak value of the wave will drop to as low as 2-3 volts and this is not satisfactory. By directly integrating the aforementioned waveforms in a conventional system, a tachometer would read an increasing function resulting from the increased number of pulses at high engine speeds. There would be, however, a reduced overall integral at high engine speeds due to the fall-off in voltage because of the long charging time or time constant of resistor 30 in the primary of ignition coil 13. When the circuit of box 31 is used, the on time will be extended so that at high engine speeds, the peak output of the exponential wave remains at approximately 6 volts. By connecting the output at point 46 to capacitor 47, DC. restoring diode 48, resistor 49 and a meter or indicating device 50, current through the meter will be proportional to the engine speed. The purpose of DC. restorer diode 48 is to take the change in level, which is essentially between 12 volts plus and 6 volts plus and shift it to between zero and 6 volts. This is used so that one side of the meter can be connected directly to ground and the other side directly to point 46.

It should be apparent that changes can be made in details of the circuit and that parts of the circuit can be used for various applications without departing from the spirit of the invention except as set forth in the appended claims.

What is claimed is:

1. In a circuit having a periodically and mechanically operated electric switch and a source of power, the combination including load means, means connecting said load means in series between said source of power and said switch, and normally open bypass circuit means connected in parallel with said switch, said bypass circuit means having a time-delay means therein, said bypass circuit being operable to directly shunt said switch and again furnish current to said load a predetermined time after said switch means opens each time.

2. In a circuit having a periodically and mechanically operated electric switch and a source of power, the combination inductive load means, means connecting said load means in series between said source of power and said switch, normally open bypass circuit means connected in parallel with said switch, said bypass circuit means having a time-delay means therein, said bypass circuit being operable to directly shunt said switch and again furnish current to said load a predetermined time after said switch means opens each time, and means opening said bypass circuit when said switch closes.

3. In a circuit having a periodically and mechanically operated electric switch and a source of power, the combination including inductive load means, means connecting said load means in series between said source of power and said switch, transistor means between said switch and load, means providing forward bias to said transistor means when said switch is closed so as to render said transistor conducting, means providing reverse bias to said transistor when said switch opens so as to shut off conduction by said transistor means, normally open bypass circuit means connected in parallel with said switch. said bypass circuit means having a time-delay means therein, said bypass circuit being operable to directly shunt said switch and again furnish current to said load a predetermined time after said switch means open each time, and means opening said bypass circuit when said switch closes.

4. In a circuit having a periodically and mechanically operated electric switch and a source of power, the combination including inductive load means, means connecting said load means in series between said source of power by said switch, normally open bypass circuit means connected in parallel with said switch, said bypass circuit means having a time-delay means therein, solid state switching means in said bypass circuit operable at the end of a predetermined time after said switch opens to directly shunt said switch and again furnish current to said load before said switch again closes, and means opening said bypass circuit when said switch closes.

5. In an engine ignition system having an interrupter switch and a source of DC. power, the combination including an ignition coil, transistor means, means connecting said transistor means, ignition coil, source of power and switch in series, forward biasing means connected to said transistor for rendering the transistor conducting when said switch is closed, normally open bypass circuit means connected in parallel to said switch having a timedelay means therein, said circuit means being closed a predetermined time after said switch opens so as to shunt said switch and cause current to flow through said ignition coil before said switch again closes, said bypass circuit means being opened when said switch is closed after having been opened.

6. In a engine ignition system having an interrupter switch and a source of DC. power, the combination including an ignition coil, transistor means, means connect ing said transistor means, ignition coil, source of power and switch in series, forward biasing means connected to said transistor for rendering the transistor conducting when said switch is closed, normally open bypass circuit means connected in parallel to said switch having a timedelay means therein, and solid state switching means in said bypass circuit, said solid state switching means becoming conductive so that said bypass circuit means will be closed a predetermined time after said switch opens so as to shunt said switch and cause current to flow through said ignition coil before said switch again closes, said bypass circuit means being opened when said switch is closed after having been opened.

7. The combination of claim 5 wherein said time-delay means includes a capacitor and resist-or.

8. In an engine ignition system, the combination including an ignition coil, a solid state device having a base, collector and emitter means, a source of DC. connected to one of said base, collector and emitter means through said ignition coil, a mechanically operated interrupter switch connected with one of said base, collector and emitter means, a reverse-biasing diode circuit means connected to said interrupter switch and across said base and emitter means, means connecting a reference voltage means between said base means and ground, and means furnishing forward bias to said solid state device when said switch is closed, so that when said switch is closed, current will flow through said ignition coil and when open, current will stop flowing until again rendered conducting.

9. In an engine ignition system, the combination including an ignition coil, a solid state device having a base, collector and emitter means, a source of DC. connected to one of said base, collector and emitter means through said ignition coil, a mechanically operated interrupter switch connected with one of said base, collector and emitter means, a reverse-biasing diode circuit means connected to said interrupter switch and across said base and emitter means, means connecting a reference voltage means between said base means and ground, means furnishing forward bias to said solid state device when said switch is closed so that when said switch is closed, current will flow through said ignition coil and when open, current will stop flowing until again rendered conducting, and bypass circuit means connected in parallel with said switch, said bypass circuit means having a time-delay means therein, said bypass circuit means being operable to again furnish current to said load a predetermined time after said switch means opens each time.

10. In an engine ignition system, the combination including a source of DO, an ignition coil connected thereto, a transistor connected to said ignition coil, an interrupter switch connected to said transistor, said source, coil transistor and switch being connected in series, means connecting said DC. to said transistor providing a forward bias to render the same conductive when said switch is closed, reverse bias means connected between said transistor and switch to provide turn off voltage to said transistor when said switch opens after being closed, a bypass circuit means connected across said switch for energizing said transistor, and time-delay means in said bypass circuit means operable upon opening of said switch to provide a shunt path around said switch a predetermined time after opening and before the next closing of said switch.

11. In an engine ignition system, the combination including a source of D.C., an ignition coil connected thereto, a transistor connected to said ignition coil, an interrupter switch connected to said transistor, means connecting said DC. to said transistor providing a forward bias to render the same conductive when said switch is closed, reverse bias means connected between said transister and switch to provide turn off voltage to said transist-or when said switch opens after being closed, a bypass circuit connected across said switch for energizing the same, said bypass circuit having transistor means therein, and time-delay means in said bypass circuit operable upon opening of said switch to provide a path around said switch by causing said transistor means to become conducting a predetermined time after opening and before the next closing of said switch.

12. In an engine ignition and tachometer system having an interrupter switch and a source of DC. power, the combination including an ignition coil, transistor means connected to said ignition coil, means connecting said transistor and coil in series with said source of power and switch, forward biasing means connected to said transistor and switch for causing said transistor to conduct when said switch closes, reverse biasing means for rendering said transistor nonconductive upon opening of said switch, normally open bypass circuit means connected in parallel with said switch and having a time-delay means therein operable upon opening said switch to close a shunt circuit directly bypassing said switch and to reenergize said transistor a predetermined time after said switch opens and before it again closes, said bypass circuit again opening when said switch closes, and a tachometer circuit connected to the circuit through said transistor for receiving a signal when the transistor is conducting.

13. The combination defined in claim 12 wherein said tachometer circuit includes a differentiating means and rectifying means.

'14. The combination defined in claim 12 wherein said tachometer circuit is connected to a junction between said coil and said source, and said tachometer circuit includes a DO restoring means.

15. In an engine ignition system, the combination including an ignition coil, a solid state device having a base, collector and emitter means, a source of DC. connected to one of said base, collector and emitter means through said ignition coil, a mechanically operated interrupter switch connected with one of said base, collector and emitter means, a reverse-biasing diode circuit means connected to said interrupter switch and across said base and emitter means, means connecting a reference voltage means between said base means and ground, means furnishing forward bias to said solid state device when said switch is closed so that when said switch is closed, current will ilow through said ignition coil and when open, current will stop flowing until again rendered conducting, and bypass circuit means connected in parallel with said switch, said bypass circuit means having a capacitor resistance time-delay network therein, said bypass circuit being operable to again furnish current to said load a predetermined time after said switch means opens each time.

16. The combination defined in claim 4 wherein said solid state switching means comprises a transistor.

References Cited UNITED STATES PATENTS 3,087,090 4/1963 Konopa 123148 3,144,012 8/1964 Tarter l23148 3,213,320 10/1965 Worrell 123-148 LAURENCE MpGOODRIDGE, Primary Examiner.

Disclaimer 3,363,615.Ge0rge Ill. .Meyerle, South Ozone Park, N.Y. S\VITCHING CIR- CUIT. Patent dated Jan. 16, 1968. Disclaimer filed Nov. 2, 1977, by the assignee, BSR (USA )Ltd. Hereby enters this disclaimer to the remaining term of said patent.

[Oficz'al Gazette January 17, 1.978.] 

